1. Field of the Invention
The present invention relates to a pressure control valve applied to a fuel injection equipment of an internal combustion engine, more particularly to a structure for making the pressure control valve small-sized.
2. Prior Art
In a fuel injection equipment of an internal combustion engine of an automobile, there is provided a pressure control valve for controlling pressure of fuel which is injected to an intake pipe. The pressure control valve is a pressure relief valve for discharging fuel based on the balance between intake negative pressure, a control spring and fuel pressure in order to obtain fuel pressure corresponding to the intake negative pressure.
An example of a prior art pressure control valve will be now described with reference to FIG. 9 which is a cross-sectional view thereof.
The pressure control valve includes a fuel inlet passage 2, a fuel outlet passage 3 and an introduction passage 4 for intake negative pressure. A valve body 1 comprises an upper casing 1A and a lower casing 1B wherein a diaphragm 5 is held and clamped between the upper casing 1A and lower casing 1B. An end of the fuel outlet passage 3 forms a valve seat 6 which is opened or closed by a flat-plate shaped valve body 7. The diaphragm 5 is penetrated to provide a holding member 8. A hole 10 is provided at the center of the holding member 8 for receiving a ball 9 to which the valve body 7 is fixed. The ball 9 is prevented from slipping off by a retaining member 11 and it is universally rotatable. A presser spring 12 is provided between the ball 9 and the bottom of the hole 10 for preventing the inclination of the valve body 7 by pressing the valve body 7 toward the valve seat 6. A conical member 13 is provided on the holding member 8 for clamping the diaphragm 5. A control spring 14 is provided inside an upper casing 1A on the conical member 13 for pressing the diaphragm 5 downward (in the direction to close the valve seat 6 by the valve body 7). The diaphragm 5 is held by the valve body 1 by putting a deformation prevention member 15 and once caulking the deformation prevention member 15 by the upper end of the lower casing 1B, then putting the lower end of the upper casing 1A on the caulked upper end of the lower casing 1B and caulking the upper end of the lower casing 1B by the lower end of the upper casing 1A. The intake negative pressure is introduced from an internal combustion engine (not shown) into a negative pressure chamber 16 in a space above the diaphragm 5 through the introduction passage 4. A seal 17 is provided between the caulked portion between the upper casing 1A and lower casing 1B for assuring the sealing of the negative pressure chamber 16.
The prior art pressure control valve operates as follows.
The fuel flows from the fuel inlet passage 2 and always acts upon the diaphragm 5 and holding member 8. When the valve body 7 opens the valve seat 6 due to the functional relation between the fuel pressure and intake negative pressure acting upon the control spring 14 and the upper side of the diaphragm 5, the fuel reaches the fuel outlet passage 3 and flows out from the fuel outlet passage 3. Since the holding member 8 which is vertically movably held by the diaphragm 5 is not always centered, the valve body 7 can surely close the valve seat 6 when the ball 9 is universally rotated.
In the prior art pressure control valve, when the load to be applied to the diaphragm 5 by the control spring 14 (hereinafter referred to as a setting load) is set after assembling automobile parts, the setting value is adjusted by plastically deforming the surface of the upper casing 1A by an external force FA, for example, by plastically deforming the surface of the upper casing 1A from the state as illustrated by broken lines to the state as illustrated by solid lines.
The intake negative pressure acts upon the upper surface of the diaphragm 5 comprising two adhered members and fuel pressure acts upon the lower surface of the diaphragm 5. Accordingly, force FB to open the caulked portion acts upon the caulked portion of the diaphragm 5, whereby the diaphragm 5 is liable to be slipped off. However, since the deformation prevention member 15 is provided, the caulked portion of the diaphragm 5 is prevented from being opened and slipped off by rigidity of the deformation prevention member 15.
Further, if the diaphragm 5 is made of rubber alone, the diaphragm 5 is deteriorated because rubber is swelled by the fuel. Accordingly, there is proposed a diaphragm having a double structure, i.e. made of rubber which is backed by an oil resistant synthetic resin film.
Automobiles are now required to be small-sized and light-weighted. To meet these requirements, each part constituting the automobile parts (hereinafter referred to as simply parts) is necessary to be small-sized and the number of parts must be reduced. If the parts are small-sized, the assembly of the parts becomes difficult and complicated. Accordingly, the parts must be structured so as to be small-sized and easily assembled.
However, according to the structure of the prior art pressure control valve, there are the following problems for making it small-sized and light-weighted.
When the pressure control valve is made small-sized in the direction of its diameter in FIG. 10, an interval L between the control spring 14 and one side of the upper casing 1A is reduced. If the interval L is reduced, it is impossible to assure the length H which is necessary for sufficient deformation of the upper casing 1A even if the setting load of the control spring 14 is adjusted by plastically deforming the top surface of the upper casing 1A by the external force FA. Accordingly, it is substantially impossible to adjust the setting load.
Further, when the diameter of the pressure control valve is reduced, the diameter of the upper casing 1A is also reduced so that it takes large load to deform cornered portion of the upper casing 1A.
Accordingly, with the structure of the prior art pressure control valve, the fact that the sufficient length H for deforming is not assured and the load necessary for deformation is increased become obstacles to make the pressure control valve small-sized.
According to the structure of the holding member 8 and valve body 7 of the prior art pressure control valve, since the holding member 8 swings in the direction of arrow S in FIG. 9, it is difficult to attach the diaphragm 5. This difficulty is increased when the pressure control valve is made more small-sized. Since the swing of the holding member 8 in the direction of arrow S occurs during the operation of the pressure control valve, the valve body 7 insufficiently closes the valve seat 6, which causes partial abrasion of the valve body 7 or valve seat 6.
Further, according to the arrangement of the holding member 8 and valve body 7 of the pressure control valve, since the conical member 13 and presser spring 12 are provided, the number of parts is reduced, which increases the difficulty of assembly of the parts and obstructs to make the pressure control valve small-sized.
Still further, according to the arrangement of the prior art pressure control valve, since the caulked portion between of the diaphragm 5 is prevented from being opened by the upward force FB which acts upon the diaphragm 5, the deformation prevention member 15 is provided. This requires the seal 17, which increases the number of parts. Accordingly, when the pressure control valve is made small-sized, the assembly of the parts is made difficult and costs high, which obstructs making the pressure control valve small-sized.
With the arrangement of the proposed pressure control valve, since the diaphragm 5 is made of rubber which is backed by an oil resistant synthetic resin film, there is a likelihood of generation of curling, i.e., bending of the diaphragm 5 due to the difference of contraction rate of rubber and synthetic resin film. The curling is generated in such a flat diaphragm pressure control valve and particularly, it becomes large at the outer periphery of the diaphragm. If such curling is generated, it is substantially impossible to caulk the diaphragm 5 of the small-sized pressure control valve.